1. Field of the Invention
The present invention relates to the field of displaying technology, and in particular to a driving device and a driving method of an active matrix organic light-emitting diode (AMOLED).
2. The Related Arts
Flat panel displays have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus widely used. Currently available flat panel displays generally include liquid crystal displays (LCDs) and organic light emitting displays (OLEDs).
Organic light emitting displays (OLEDs) have a variety of superior properties, such as being self-luminous, requiring no backlighting, high contrast, reduced thickness, wide view angle, fast response, applicability to flexible panels, wide range of operation temperature, and having simple structure and manufacturing process, and are regarded as emerging technology of the next generation flat panel displays.
The OLEDs can be classified, according to the type of driving, as passive OLEDs (such as passive matrix OLEDs (PMOLEDs)) and active OLEDs (such as active matrix OLEDs (AMOLEDs)). The AMOLEDs belong to the type of active displaying and have a display panel on which pixel structures are provided in an arrangement of an array.
An AMOLED pixel structure is generally composed of two transistors in combination with a storage capacitor for storing electrical charges in order to control brightness performance of an organic light emitting diode. The organic light emitting diode is a current driving device, which generates different brightness of light according to the magnitude of electrical current flowing therethrough.
FIG. 1 is a schematic view illustrating an AMOLED pixel structure. The pixel structure comprises a driving portion and a light emitting portion, wherein the driving portion comprises a first transistor T1, a second transistor T2, and a storage capacitor CS and the light emitting portion comprises an organic light emitting diode D. The first transistor T1 has a drain electrode that receives a data signal Data, a gate electrode that receives a scan signal Scan, and a source electrode electrically connected to a gate electrode of the second transistor T2. The scan signal Scan controls the conduction of the first transistor T1. The second transistor T2 has a drain electrode electrically connected with a positive potential OVDD of a power source and a source electrode electrically connected to a positive terminal of the organic light emitting diode D. The organic light emitting diode D has a negative terminal electrically connected to a negative potential OVSS of the power source. The capacitor CS has an end electrically connected to the gate electrode of the second transistor T2 and an opposite end electrically connected to the drain electrode of the second transistor T2.
In carrying out a driving operation with a conventional AMOLED driving device, two adjacent normal frames of image are sequentially displayed. When the scan signal Scan is a low level signal, the first transistor T1 is shut down to prohibit the voltage across the two ends of the storage capacitor CS from discharging through the first transistor and theoretically, the voltage across the two ends of the storage capacitor CS can maintain unchanged, so that the second transistor T2 keeps the organic light emitting diode D continuously emitting light until the arrival of the data signal Data of the second frame. Being cycled in this way easily causes interference of the data signal displayed in the current frame by the data signal of the previous frame, resulting in a displaying defect of residual image. Further, in case that the time period within which the same image is displayed is excessively extended, shifting of the threshold voltage of the second transistor T2 may easily result.